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To see examples of how to cable dual storage IOA configurations, see Serial attached SCSI cable planning.
Note: Some systems have SAS RAID adapters integrated onto the system boards. Separate SAS cables are
not required to connect the two integrated SAS RAID adapters to each other.
Related concepts:
"Installing dual storage IOA configurations" on page 30
Use this procedure to install a dual storage I/O adapter (IOA) configuration.
Related information:
Serial attached SCSI cable planning
Performance considerations
Controller failures can affect performance.
The controller is designed to minimize performance impacts when running in a dual storage IOA
configuration. When using RAID 5 and RAID 6, parity footprints are mirrored between the controller's
nonvolatile memory, which causes only a slight impact to performance. For controllers with write cache,
all cache data is mirrored between the controller's nonvolatile memories, which also causes only a slight
impact to performance.
If one controller fails in a dual storage IOA configuration, the remaining controller disables write caching
(if auxiliary cache is not also provided by the controllers) and begins to keep an additional copy of parity
footprints on disk. This can significantly affect performance, particularly when using RAID 5 and RAID 6.
Dual storage IOA access optimization
View the active or passive path of your disk units and controller.
Dual storage IOA access characteristics can balance the controller workload. The dual storage IOA access
characteristics for a disk array, parity set, specifies which controller is preferred to be optimized for the
disk array. It performs direct read and write operations to the physical devices. The controller that is
preferred to be optimized for the disk array, contains the active path to the disk units in the disk array.
The other controller contains the passive path. The system only sends read and write operations down
the active path. The passive path is only used if the active path fails.
Best performance is achieved when the dual storage IOA access characteristics on each disk array have a
balanced workload. This happens when the two controllers have an equal number of disk arrays with
active paths to the disk units.
The system selects the disk units and dual storage IOA access characteristics for each disk array. When
creating disk arrays, set the parity set optimization to Performance. This attribute sets an even number of
disk arrays (for example, 2, 4, 6, and so forth) to be created. It also enables the system to optimize disk
arrays on each controller. As a result, the two controllers will have an equal number of disk units with an
active path.
To change the parity set optimization, see Changing parity set optimization.
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SAS RAID controllers for IBM i
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